1,813 research outputs found
Compositional abstraction and safety synthesis using overlapping symbolic models
In this paper, we develop a compositional approach to abstraction and safety
synthesis for a general class of discrete time nonlinear systems. Our approach
makes it possible to define a symbolic abstraction by composing a set of
symbolic subsystems that are overlapping in the sense that they can share some
common state variables. We develop compositional safety synthesis techniques
using such overlapping symbolic subsystems. Comparisons, in terms of
conservativeness and of computational complexity, between abstractions and
controllers obtained from different system decompositions are provided.
Numerical experiments show that the proposed approach for symbolic control
synthesis enables a significant complexity reduction with respect to the
centralized approach, while reducing the conservatism with respect to
compositional approaches using non-overlapping subsystems
Lattice calculation of the pion transition form factor with Wilson quarks
We present a lattice QCD calculation of the double-virtual neutral pion
transition form factor, with the goal to cover the kinematic range relevant to
hadronic light-by-light scattering in the muon . Several improvements have
been made compared to our previous work. First, we take into account the
effects of the strange quark by using the CLS gauge ensembles.
Secondly, we have implemented the on-shell -improvement of the
vector current to reduce the discretization effects associated with Wilson
quarks. Finally, in order to have access to a wider range of photon
virtualities, we have computed the transition form factor in a moving frame as
well as in the pion rest-frame. After extrapolating the form factor to the
continuum and to physical quark masses, we compare our results with
phenomenology. We extract the normalization of the form factor with a precision
of 3.5\% and confirm within our uncertainty previous somewhat conflicting
estimates for a low-energy constant that appears in chiral perturbation theory
for the decay at NLO. With additional input from
experiment and theory, we reproduce recent estimates for the decay width
. We also study the asymptotic large-
behavior of the transition form factor in the double-virtual case. Finally, we
provide as our main result a more precise model-independent lattice estimate of
the pion-pole contribution to hadronic light-by-light scattering in the muon
: . Using
in addition the normalization of the form factor obtained by the PrimEx
experiment, we get the lattice and data-driven estimate
.Comment: 29 pages, 14 figures. v2: minor corrections to match the published
version. A file with the transition form factor data at the physical pion
mass and in the continuum is included in the submissio
Importance of interorbital charge transfers for the metal-to-insulator transition of BaVS
The underlying mechanism of the metal-to-insulator transition (MIT) in
BaVS is investigated, using dynamical mean-field theory in combination with
density functional theory. It is shown that correlation effects are responsible
for a strong charge redistribution, which lowers the occupancy of the broader
\a1g band in favor of the narrower bands. This resolves several
discrepancies between band theory and the experimental findings, such as the
observed value of the charge-density wave ordering vector associated with the
MIT, and the presence of local moments in the metallic phase.Comment: improved discussion, new figure, added reference
Exploratory studies for the position-space approach to hadronic light-by-light scattering in the muon
The well-known discrepancy in the muon between experiment and theory
demands further theory investigations in view of the upcoming new experiments.
One of the leading uncertainties lies in the hadronic light-by-light scattering
contribution (HLbL), that we address with our position-space approach. We focus
on exploratory studies of the pion-pole contribution in a simple model and the
fermion loop without gluon exchanges in the continuum and in infinite volume.
These studies provide us with useful information for our planned computation of
HLbL in the muon using full QCD.Comment: 8 pages, 11 figures, 1 table, Lattice 2017 proceedings, Granada,
Spai
A Logic of Reachable Patterns in Linked Data-Structures
We define a new decidable logic for expressing and checking invariants of
programs that manipulate dynamically-allocated objects via pointers and
destructive pointer updates. The main feature of this logic is the ability to
limit the neighborhood of a node that is reachable via a regular expression
from a designated node. The logic is closed under boolean operations
(entailment, negation) and has a finite model property. The key technical
result is the proof of decidability. We show how to express precondition,
postconditions, and loop invariants for some interesting programs. It is also
possible to express properties such as disjointness of data-structures, and
low-level heap mutations. Moreover, our logic can express properties of
arbitrary data-structures and of an arbitrary number of pointer fields. The
latter provides a way to naturally specify postconditions that relate the
fields on entry to a procedure to the fields on exit. Therefore, it is possible
to use the logic to automatically prove partial correctness of programs
performing low-level heap mutations
Counting LTL
The original publication is available at ieeexplore.ieee.org.International audienceThis paper presents a quantitative extension for the linear-time temporal logic LTL allowing to specify the number of states satisfying certain sub-formulas along paths. We give decision procedures for the satisfiability and model checking of this new temporal logic and study the complexity of the corresponding problems. Furthermore we show that the problems become undecidable when more expressive constraints are considered
Counting CTL
The original publication is available at www.springerlink.com.International audienceThis paper presents a range of quantitative extensions for the temporal logic CTL. We enhance temporal modalities with the ability to constrain the number of states satisfying certain sub-formulas along paths. By selecting the combinations of Boolean and arithmetic operations allowed in constraints, one obtains several distinct logics generalizing CTL. We provide a thorough analysis of their expressiveness and of the complexity of their model-checking problem (ranging from P-complete to undecidable)
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